The present invention relates generally to the management of transitions between different firing patterns used during skip fire operation of an engine.
Skip fire engine control is understood to offer a number of benefits including the potential of increased fuel efficiency. In general, skip fire engine control contemplates selectively skipping the firing of certain cylinders during selected firing opportunities. Thus, for example, a particular cylinder may be fired during one firing opportunity and then may be skipped during the next firing opportunity and then selectively skipped or fired during the next. This is contrasted with conventional variable displacement engine operation in which a fixed set of the cylinders are deactivated during certain low-load operating conditions.
Many skip fire controllers are arranged to provide a set of available firing patterns or firing fractions. In some circumstances the set of available firing patterns or fractions will vary as a function of various operating parameters such as engine load or speed. Typically the available firing patterns are selected, in part, based on their vibration characteristics. Although careful selection of the available firing patterns helps facilitate smooth operations, transitions between different firing patterns can cause undesirable noise, vibration and harshness (NVH) concerns. Therefore, there are continuing efforts to provide improved schemes for transitioning between different firing patterns or different firing fractions.